Zoom lenses with a focal range below 50mm are known as wide-angle zooms. Like wide angle prime lenses with fixed focal lengths, these capture bigger views than normal lenses, which is useful whether you’re trying to photograph a large building from inside or out, a sweeping landscape view, or even just a big group shot. They’re invaluable when you can’t step back any further.

By squeezing more into your photos, wide angle zooms inevitably have greater distortion, especially towards the edges. This may not be noticeable on natural landscapes, but can appear unflattering on portrait shots unless the person (or people) are placed in the middle of the frame. That said, this effect can also produce pleasing results and be used to exaggerate perspective – a popular wide angle technique is to get very close to a foreground subject so it appears large compared to the background. Wide angle zooms also have large depths of field, which means it’s easier to get lots in sharp focus from close-up to far away.

28mm is the most common wide angle focal length and can produce quite natural-looking results. Focal lengths above this approach a more standard view, while shorter focal lengths produce wider results. A wide-angle zoom will generally cover a variety of focal lengths from modest wide to ultra wide, giving you greater flexibility than a fixed focal length prime lens – a typical range could be 17-27mm.

As always, bear in mind any reduction in field due to your DSLRs sensor when choosing a lens. Sony’s APS-C models like the Alpha A200, A300, A350 and A700 have a reduction factor of 1.5x. So if you’d like coverage equivalent to 17-27mm, you’ll need to fit them with an 11-18mm lens. Full-frame bodies like the A900 have no field-reduction factor, so a 16-35mm lens will deliver 16-35mm coverage.

Lenses with smaller f-numbers gather more light thanks to their bigger apertures, which makes them better in dim conditions and for minimising the depth-of-field. Bigger apertures however mean a larger, heavier and more expensive lens.

Note: Sony's DT lenses are not corrected for the larger sensors of full-frame DSLRs. For a full explanation of lens specifications and examples of coverage at different focal lengths, check out our Camera Labs Lens Buyers Guide.